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McGaw I.J.,Bamfield Marine Sciences Center | Whiteley N.M.,Bangor University
Journal of Thermal Biology | Year: 2012

The effects of temperature acclimation and acute temperature change were investigated in postprandial green shore crabs, Carcinus maenas. Oxygen uptake, gut contractions and transit rates and digestive efficiencies were measured for crabs acclimated to either 10°C or 20°C and subsequently exposed to treatment temperatures of 5, 15, or 25°C. Temperature acclimation resulted in a partial metabolic compensation in unfed crabs, with higher oxygen uptake rates measured for the 10°C acclimated group exposed to acute test temperatures. The Q 10 values were higher than normal, probably because the acute temperature change prevented crabs from fully adjusting to the new temperature. Both the acclimation and treatment temperature altered the characteristics of the specific dynamic action (SDA). The duration of the response was longer for 20°C acclimated crabs and was inversely related to the treatment temperature. The scope (peak oxygen consumption) was also higher for 20°C acclimated crabs with a trend towards an inverse relationship with treatment temperature. Since the overall SDA (energy expenditure) is a function of both duration and scope, it was also higher for 20°C acclimated crabs, with the highest value measured at the treatment temperature of 15°C. The decline in total SDA after acute exposure to 5 and 25°C suggests that both cold stress and limitations to oxygen supply at the temperature extremes could be affecting the SDA response. The contractions of the pyloric sac of the foregut region function to propel digesta through the gut, and contraction rates increased with increasing treatment temperature. This translated into faster transit rates with increasing treatment temperatures. Although pyloric sac contractions were higher for 20°C acclimated crabs, temperature acclimation had no effect on transit rates. This suggests that a threshold level in pyloric sac contraction rates needs to be reached before it manifests itself on transit rates. Although there was a correlation between faster transit times and the shorter duration of the SDA response with increasing treatment temperature, transit rates do not make a good proxy for calculating the SDA characteristics. The digestive efficiency showed a trend towards a decreasing efficiency with increasing treatment temperature; the slower transit rates at the lower treatment temperatures allowing for more efficient nutrient absorption. Even though metabolic rates of 10°C acclimated crabs were higher, there was no effect of acclimation temperature on digestive efficiency. This probably occurred because intracellular enzymes and digestive enzymes are modulated through different control pathways. These results give an insight into the metabolic and digestive physiology of Carcinus maenas as it makes feeding excursions between the subtidal and intertidal zones. © 2012. Source

McGaw I.J.,Memorial University of Newfoundland | McGaw I.J.,Bamfield Marine Sciences Center | Curtis D.L.,Canadian Department of Fisheries and Oceans
Journal of Comparative Physiology B: Biochemical, Systemic, and Environmental Physiology | Year: 2013

This article reviews the mechanical processes associated with digestion in decapod crustaceans. The decapod crustacean gut is essentially an internal tube that is divided into three functional areas, the foregut, midgut, and hindgut. The foregut houses the gastric mill apparatus which functions in mastication (cutting and grinding) of the ingested food. The processed food passes into the pyloric region of the foregut which controls movement of digesta into the midgut region and hepatopancreas where intracellular digestion takes place. The movements of the foregut muscles and gastric mill are controlled via nerves from the stomatogastric ganglion. Contraction rates of the gastric mill and foregut muscles can be influenced by environmental factors such as salinity, temperature, and oxygen levels. Gut contraction rates depend on the magnitude of the environmental perturbation and the physiological ability of each species. The subsequent transit of the digesta from the foregut into the midgut and through the hindgut has been followed in a wide variety of crustaceans. Transit rates are commonly used as a measure of food processing rates and are keys in understanding strategies of adaptation to trophic conditions. Transit times vary from as little as 30 min in small copepods to over 150 h in larger lobsters. Transit times can be influenced by the size and the type of the meal, the size and activity level of an animal and changes in environmental temperature, salinity and oxygen tension. Ultimately, changes in transit times influence digestive efficiency (the amount of nutrients absorbed across the gut wall). Digestive efficiencies tend to be high for carnivorous crustaceans, but somewhat lower for those that consume plant material. A slowing of the transit rate allows more time for nutrient absorption but this may be confounded by changes in the environment, which may reduce the energy available for active transport processes. Given the large number of articles already published on the stomatogastric ganglion and its control mechanisms, this area will continue to be of interest to scientists. There is also a push towards studying animals in a more natural environment or even in the field and investigation of the energetic costs of the components of digestion under varying biotic and environmental conditions will undoubtedly be an area that expands in the future. © 2012 Springer-Verlag Berlin Heidelberg. Source

Neufeld C.J.,University of Alberta | Neufeld C.J.,Bamfield Marine Sciences Center
Journal of Experimental Zoology Part B: Molecular and Developmental Evolution | Year: 2011

Traits can evolve both in response to direct selection and in response to indirect selection on other linked traits. Although the evolutionary significance of coupled traits (e.g., through shared components of developmental pathways, or through competition for shared developmental resources) is now well accepted, we know comparatively little about how developmental coupling may restrict the independent responses of two or more phenotypically plastic traits in response to conflicting environmental cues. Such studies are important because coupled development, if present, could act as an important limit to the evolution of functionally independent plasticity in multiple traits. I tested whether developmental coupling can restrict the direction of plastic responses by studying how penis form and leg form-both highly plastic traits of barnacles-varied in response to differences in conspecific density and water velocity. Penis length and leg length in Balanus glandula varied in parallel with variation in wave-exposure but varied in opposite directions with variation in conspecific density. This study represents one of the rare tests of developmental coupling between multiple (demonstrably adaptive) plastic traits: Barnacle legs and penises appear to exhibit modular development that can respond concurrently-yet in independent directions-to conflicting environmental cues. Copyright © 2011 Wiley-Liss, Inc., A Wiley Company. Source

Szuroczki D.,Brock University | Szuroczki D.,University of Toronto | Richardson J.M.L.,Brock University | Richardson J.M.L.,Bamfield Marine Sciences Center
PLoS ONE | Year: 2012

Organisms are exposed to strong selective pressures from several sources, including predators and pathogens. Response to such interacting selective pressures may vary among species that differ in life history and ecology in predictable ways. We consider the impact of multiple enemies (fish predators and trematode parasites) on the behavior of larvae of three anuran species (Lithobates (= Rana) sylvaticus, L. clamitans and L. catesbeianus). We show that the three ranid species differ in response to the trade-off imposed by the simultaneous presence of fish predators and trematode parasites in the environment. Two more permanent pond breeders (L. clamitans and L. catesbeianus), which commonly encounter parasites and fish, increased activity when in the combined presence of parasites and a fish predator, resulting in a relatively lower parasite encystment rate. In contrast, the temporary pond breeder (L. sylvaticus), which does not commonly encounter fish in the wild, decreased activity in the combined presence of a fish predator and parasites similar to when only the predator was present. For L. sylvaticus, this suggests that the presence of an unknown predator poses a greater threat than parasites. Further, the presence of fish along with parasites increased the susceptibility of both L. sylvaticus and L. clamitans to trematode infection, whereas parasite infection in L. catesbeianus was unaffected by the presence of fish. Unpalatability to fish may allow some species to respond more freely to attacking parasites in the presence of fish. The results from this study highlight the importance of considering multiple selective pressures faced by organisms and how this shapes their behavior. © 2012 Szuroczki, Richardson. Source

Nienhuis S.,Bamfield Marine Sciences Center
Proceedings. Biological sciences / The Royal Society | Year: 2010

As CO(2) levels increase in the atmosphere, so too do they in the sea. Although direct effects of moderately elevated CO(2) in sea water may be of little consequence, indirect effects may be profound. For example, lowered pH and calcium carbonate saturation states may influence both deposition and dissolution rates of mineralized skeletons in many marine organisms. The relative impact of elevated CO(2) on deposition and dissolution rates are not known for many large-bodied organisms. We therefore tested the effects of increased CO(2) levels--those forecast to occur in roughly 100 and 200 years--on both shell deposition rate and shell dissolution rate in a rocky intertidal snail, Nucella lamellosa. Shell weight gain per day in live snails decreased linearly with increasing CO(2) levels. However, this trend was paralleled by shell weight loss per day in empty shells, suggesting that these declines in shell weight gain observed in live snails were due to increased dissolution of existing shell material, rather than reduced production of new shell material. Ocean acidification may therefore have a greater effect on shell dissolution than on shell deposition, at least in temperate marine molluscs. Source

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